preg_replace reverse/mutual replacing on synonyms words

Question

I want to mutual or reverse replace on synonyms words. I have to give an example to tell you:

$string = 'Lorem ipsum dolor sit amet, consectetur adipiscing elit';
$find = array('/ipsum/', '/amet/');
$replace = array('amet', 'ipsum');
$output = preg_replace($find, $replace, $string);

Output is:

Lorem ipsum dolor sit ipsum, consectetur adipiscing elit

Expected output is should be like that:

Lorem amet dolor sit ipsum, consectetur adipiscing elit

So i want to change all ipsum to amet and amet to lorem. These two words that "ipsum" and "amet" just samples. I have thousands synonyms words.

Like you see, i tried preg_replace function but doest work.

Answer 1

use strtr:

$string = 'Lorem ipsum dolor sit amet, consectetur adipiscing elit';
$find = array('ipsum', 'amet');
$replace = array('amet', 'ipsum');
$trans = array_combine($find, $replace);

$result = strtr($string, $trans);

The main difference with str_replace is that string is parsed only once, when str_replace (or preg_replace) parses it once for each item.

Not very interesting for you example but you can do it to with preg_replace_callback:

$trans = ['ipsum' => 'amet', 'amet'=>'ipsum'];
$result = preg_replace_callback('~amet|ipsum~', function ($m) use ($trans) {
    return $trans[$m[0]]; }, $string);

If you want to achieve the same with str_replace or preg_replace you need to use a placeholder:

$find = ['ipsum', 'amet', '###placeholder###'];
$replace = ['###placeholder###', 'ipsum', 'amet'];
$result = str_replace($find, $replace, $string);